JP5984503B2 - Tractor exhaust system - Google Patents

Description

  The present invention mixes a first exhaust passage through which exhaust from an engine is circulated, an outside air introduction portion that introduces outside air, exhaust gas that has circulated through the first exhaust passage, and outside air introduced from the outside air introduction portion. The present invention relates to an exhaust device for a tractor including a second exhaust passage that exhausts to the outside.

  The exhaust apparatus as described above reduces the exhaust temperature by mixing the exhaust air flowing through the first exhaust passage with the outside air introduced from the outside air introduction section, and the exhaust gas whose temperature has been reduced is supplied to the second exhaust passage. To exhaust outside.

  In the conventional exhaust system, both the first exhaust path and the second exhaust path are configured by a flow pipe through which fluid can freely flow, and the inner diameter of the flow pipe is larger in the second exhaust path than in the first exhaust path. The diameter is also large. Then, in the exhaust flow direction, the downstream end portion of the first exhaust passage is located downstream of the upstream end portion of the second exhaust passage so that the first exhaust passage is inward and the second exhaust passage is A double tube structure is used as the outside (see, for example, Patent Document 1).

  In the exhaust device described in Patent Document 1, an opening formed between the outer peripheral portion of the first exhaust passage and the inner peripheral portion of the second exhaust passage is formed at the upstream end portion of the second exhaust passage. As the exhaust gas flowing through the first exhaust passage flows into the second exhaust passage, outside air is introduced from the outside air introduction portion due to the ejector effect associated with the inflow. The outside air introduced from the outside air introduction portion flows in a gap formed between the outer peripheral portion of the first exhaust passage and the inner peripheral portion of the second exhaust passage in the double pipe structure, and then the second exhaust passage. It is mixed with the exhaust that circulates.

Japanese Utility Model Publication No. 2-47215

  In the exhaust device described in Patent Literature 1, the outside air introduced from the outside air introduction portion is formed between the outer peripheral portion of the first exhaust passage and the inner peripheral portion of the second exhaust passage in the double pipe structure. Since it circulates through the gap, the outside air is heated by the exhaust gas flowing through the first exhaust passage while circulating around the outer periphery of the first exhaust passage. Therefore, the outside air whose temperature has risen due to the heating is then mixed with the exhaust gas, and the exhaust gas temperature may not be effectively reduced.

  Further, as described in Patent Document 1, in the case of adopting the double pipe structure, when the outside air is introduced from the outside air introduction portion, the first exhaust passage located inside becomes a resistance, and the outside air introduction portion It is difficult to introduce a sufficient amount of outside air, and there is a possibility that the exhaust temperature cannot be effectively reduced from this point.

  The present invention has been made paying attention to this point, and an object of the present invention is to provide an exhaust device for a tractor that can effectively lower the exhaust temperature and facilitate the assembly of the exhaust passage. is there.

In order to achieve this object, the characteristic configuration of the exhaust device for a tractor according to the present invention includes a first exhaust passage through which exhaust from the engine is circulated, an outside air introduction portion for introducing outside air, and a circulation through the first exhaust passage. A tractor exhaust device comprising: a second exhaust path that mixes the exhausted air and the outside air introduced from the outside air introduction unit and exhausts the mixture to the outside;
The first exhaust path and the second exhaust path are disposed in a state where the downstream end of the first exhaust path and the second exhaust path extend in the front-rear direction,
The flow passage cross-sectional area of the second exhaust passage is configured to be larger than the first exhaust passage,
The positional relationship in the flow direction of the exhaust between the first exhaust path and the second exhaust path is such that the outer periphery at the downstream end of the first exhaust path and the inner periphery at the upstream end of the second exhaust path. Or the first exhaust passage so that the downstream end portion of the first exhaust passage and the upstream end portion of the second exhaust passage are in the same position in a state where the space is open to the outside. The first exhaust passage and the second exhaust passage are provided so as to form a gap between the downstream end portion of the second exhaust passage and the upstream end portion of the second exhaust passage,
The outside air introduction portion is configured by a gap formed between an outer peripheral portion at a downstream end portion of the first exhaust passage and an inner peripheral portion at an upstream end portion of the second exhaust passage ,
A downstream end of the first exhaust passage and the second exhaust passage are disposed below an engine bonnet that covers the engine .

According to this configuration, the downstream end of the first exhaust passage and the upstream end of the second exhaust passage are located at the same position in the exhaust flow direction, or the downstream end of the first exhaust passage. Is formed between the outer peripheral portion of the downstream end portion of the first exhaust passage and the second exhaust passage at the upstream end portion of the second exhaust passage. A gap is formed between the inner peripheral portion of the upstream end portion of the first gas and the gap can be configured as an outside air introduction portion.
The outside air introduced from the outside air introduction part flows directly into the second exhaust path without flowing around the outer periphery of the first exhaust path. As a result, the outside air introduced from the outside air introduction section is mixed with the exhaust flowing through the second exhaust passage while being suppressed from being heated by the exhaust flowing through the first exhaust passage, so that the exhaust temperature is effectively reduced. Can be lowered.
Moreover, in the exhaust flow direction, the downstream end of the first exhaust passage and the upstream end of the second exhaust passage are in the same position, or the downstream end of the first exhaust passage and the second exhaust passage. Since the first exhaust passage is not located inside the second exhaust passage and does not become a resistance, a sufficient flow rate from the outside air introduction portion can be obtained. It becomes easy to introduce outside air, and from this point, the exhaust temperature can be effectively reduced.
In addition, when attaching the second exhaust path to the end of the first exhaust path, the first exhaust path is inserted into the second exhaust path, and it is assembled in a small space without requiring movement in the perspective direction between the exhaust paths. Therefore, the exhaust passage can be easily assembled.
In a further characteristic configuration of the exhaust device for a tractor according to the present invention, the first exhaust gas passage is formed so that a gap is formed between the downstream end portion of the first exhaust passage and the upstream end portion of the second exhaust passage. An exhaust path and the second exhaust path are provided ;
Lies in front Symbol second exhaust passage are disposed on the front side in the vehicle body longitudinal direction with respect to the first exhaust passage.

  According to a further feature of the exhaust apparatus for a tractor according to the present invention, the first exhaust path and the second exhaust path are an outer peripheral portion at a downstream end of the first exhaust path and an upstream of the second exhaust path. It exists in the point arrange | positioned so that the said external air introduction part may be formed over the perimeter of the circumferential direction between the inner peripheral parts in a side edge part.

  According to this characteristic configuration, the outside air introduction portion is disposed on the entire circumference in the circumferential direction between the outer peripheral portion at the downstream end portion of the first exhaust passage and the inner peripheral portion at the upstream end portion of the second exhaust passage. Over the air, it is possible to introduce outside air. Thereby, while being able to introduce outside air uniformly from the perimeter of the circumferential direction, it becomes easy to introduce more outside air, and it becomes easy to ensure a sufficient quantity as an introduction flow rate from an outside air introduction part.

  A further characteristic configuration of the exhaust device for a tractor according to the present invention is that a first support that supports the first exhaust path and a second support that supports the second exhaust path are provided separately. is there.

  According to this characteristic configuration, since the first support body and the second support body are separately provided, the first exhaust path and the second support body can be provided without a member connecting the first exhaust path and the second exhaust path. Both of the second exhaust passages can be arranged in an appropriate positional relationship. Therefore, the member connecting the first exhaust path and the second exhaust path does not become resistance when introducing the outside air from the outside air introduction section, and it is easy to ensure a sufficient amount as the introduction flow rate from the outside air introduction section. . Further, since the support bodies for the first exhaust path and the second exhaust path are provided separately, for example, the second support path is supported by being separated from the engine and the exhaust gas purification processing device (DPF) by the second support body. By supporting in this way, it is possible to prevent vibration transmitted from the engine through the exhaust purification processing device (DPF) from being transmitted to the second exhaust path.

  According to a further characteristic configuration of the exhaust device for a tractor according to the present invention, the cross-sectional area of the external air introduction portion is the first flow rate from the external air introduction portion with respect to the flow passage cross-sectional area of the first exhaust passage. It is in the point which becomes more than the set multiple which makes it more than the exhaust gas flow rate in the exhaust passage.

  According to this feature configuration, the flow rate of the introduction from the outside air introduction section is reduced by the cross-sectional area of the outside air introduction section being a set multiple or more than the cross-sectional area of the first exhaust path. The flow rate can be exceeded. Thereby, in the second exhaust path, the exhaust air flowing through the first exhaust path can be mixed with the outside air having a flow rate equal to or higher than the exhaust flow rate, so that the exhaust temperature can be effectively reduced.

Side view of tractor Longitudinal section showing inside of engine room Perspective view showing inside of engine room The figure which shows the principal part of the exhaust system The figure which shows the principal part of the exhaust apparatus in 2nd Embodiment. The positional relationship in the flow direction of exhaust gas between the first exhaust path and the second exhaust path, the length of the second exhaust path, and the ratio of the outside air introduction flow rate from the outside air introduction portion to the exhaust flow rate in the first exhaust path. Experimental results showing the relationship Experimental results showing the relationship between the positional relationship of the first exhaust path and the second exhaust path in the flow direction of the exhaust and the ratio of the outside air introduction flow rate to the exhaust flow rate Experimental results showing the relationship between the flow passage cross-sectional area of the first exhaust passage, the flow passage cross-sectional area of the second exhaust passage, and the ratio of the outside air introduction flow rate from the outside air introduction portion to the exhaust flow rate in the first exhaust passage. Experimental results showing the relationship between the cross-sectional area of the first exhaust path, the cross-sectional area of the second exhaust path, and the exhaust temperature Experimental results showing the relationship between the area ratio, which is the ratio of the cross-sectional area of the outside air introduction portion to the flow passage cross-sectional area of the first exhaust passage, and the ratio of the outside air introduction flow rate to the exhaust flow rate

An embodiment of an exhaust device for a tractor according to the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 shows an entire side surface of a tractor with a cabin as an example of a tractor to which a tractor exhaust device according to the present invention is applied.
This tractor includes a driving unit 1 located at the front of the vehicle body and a driving cabin 2 located at the rear of the vehicle body, and integrally connects the engine mounting frame 3, the clutch housing (not shown), and the transmission case 4. Thus, the body frame 5 is configured. The driving unit 1 and the driving cabin 2 are mounted on the body frame 5, and the body frame 5 is supported by a pair of left and right front wheels 6 and rear wheels 7.

  As shown in FIG. 2, the driving unit 1 employs a diesel engine that is supported by an anti-vibration material (not shown) on the engine mounting frame 3 in the engine room covered with the engine bonnet 8. An engine 9 is provided. FIG. 2 is a longitudinal sectional view showing the inside of the engine room. The motive power from the engine 9 is transmitted to the front wheels 6 and the rear wheels 7 through a traveling transmission system including a traveling transmission (not shown) and the like built in the transmission case 4 also serving as a frame. A four-wheel drive tractor is configured.

  At the rear part of the transmission case 4, a pair of left and right lift arms 10 that are driven to swing in the vertical direction by the operation of a hydraulic lifting cylinder (not shown) installed in the upper part, and takeout of engine power to the outside. A power take-out shaft 11 and the like are provided. The power take-off shaft 11 is connected to the engine via a work transmission system including a work transmission system (not shown), a work clutch (not shown), and the like, which are separate from the traveling transmission system built in the transmission case 4. The power from 9 is transmitted. The left and right lift arms 10 are connected to a link mechanism (not shown) connected to the rear portion of the transmission case 4 so as to be swingable up and down, and the power take-out shaft 11 is connected to the link mechanism. A transmission shaft or the like for transmitting power to a working device (not shown) such as a rotary tiller is connected.

  The driving cabin 2 has a roof frame 13 supported on a cabin frame 12 erected at four corners of the front, rear, left and right, a front glass 14 made of a transparent curved glass or the like on the front side, and a transparent glass on the left and right sides. A pair of left and right door panels 15 of an outward opening type are provided and formed in a rectangular box shape. The driving cabin 2 is provided with a steering wheel 16 and a driving seat 17.

  As shown in FIG. 2, in the prime mover 1, in the engine room, a battery 18 and a radiator 19 for cooling the engine are provided on the front side of the vehicle body of the engine 9, and a fuel tank 20 is provided on the rear side of the vehicle body of the engine 9. It has been. In the engine room, an exhaust purification treatment device 21 with a muffler function that houses an air cleaner (not shown) for engines, DOC (diesel oxidation catalyst), DPF (diesel particulate filter), and the like is provided. It has been.

  As shown in FIGS. 2 and 3, the exhaust purification processing device 21 is supported on the upper side of the engine 9 by a gate-shaped support body 22 extending upward from the engine mounting frame 3. FIG. 3 is a perspective view showing the inside of the engine room. The exhaust purification treatment device 21 captures particulate matter contained in the exhaust from the engine 9 with the DPF, oxidizes and burns unburned fuel in the exhaust with the DOC, and raises the exhaust temperature, thereby capturing the particulates captured by the DPF. The DPF is regenerated by burning the particulate material.

  Exhaust gas from the engine 9 is processed by the exhaust gas purification processing device 21, and the exhaust gas after the processing is exhausted to the outside by the exhaust device 23. As shown in FIGS. 3 and 4, the exhaust device 23 includes a first exhaust passage 24 through which exhaust H (exhaust after processing by the exhaust purification processing device 21) from the engine 9 circulates and outside air introduction for introducing outside air And a second exhaust passage 26 that mixes the exhaust H flowing through the first exhaust passage 24 and the outside air G introduced from the outside air introduction portion 25 and exhausts the mixture K to the outside.

  Both the first exhaust path 24 and the second exhaust path 26 are constituted by flow pipes through which fluid can flow freely. The cross-sectional area of the second exhaust path 26 is configured to be larger than that of the first exhaust path 24. The positional relationship in the exhaust flow direction between the first exhaust path 24 and the second exhaust path 26 is such that the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26 are The first exhaust path 24 and the second exhaust path 26 are provided so as to form a gap S (for example, about 0 to 30 mm) therebetween. The outside air introduction portion 25 is configured by a gap T formed between the outer peripheral portion at the downstream end portion 24 b of the first exhaust passage 24 and the inner peripheral portion at the upstream end portion 24 a of the second exhaust passage 26. Yes.

  The first exhaust path 24 has an upstream end 24a connected to the exhaust purification processing device 21, extends from the upper side of the engine 9 toward the lower front side of the vehicle body, and has a downstream end 24b mounted on the engine. It is arranged so as to be located laterally outside the frame 3. As shown in FIG. 4 (b), the downstream end 24b of the first exhaust passage 24 has a cross-sectional shape that is not circular but is formed in a vertically long flat shape in which the lateral side is pressed inward. Has been. Further, the second exhaust passage 26 may have a cross-sectional shape that is not circular but may have a shape that surrounds the downstream end of the first exhaust passage 24. A downstream portion of the first exhaust path 24 is supported by a first support 27, and the first support 27 is composed of a first plate member 27a and a second plate member 27b. The first plate-like member 27a is connected to the lateral side portion of the engine mounting frame 3 so as to extend in the longitudinal direction of the vehicle body. The second plate-like member 27 b has a base end that is bolted to the first plate-like member 27 a and extends outward in the lateral direction of the vehicle body, and a tip end that is connected to the first exhaust path 24.

  The second exhaust path 26 is disposed on the laterally outer side of the engine mounting frame 3 so as to extend to the front side of the vehicle body so as to be on the outer side toward the front side of the vehicle body. An intermediate portion of the second exhaust path 26 is supported by a second support 28, and the second support 28 is composed of a third plate member 28a and a fourth plate member 28b. The third plate-like member 28a is connected to a plate-like placement support 29 for placing and supporting the battery 18, and is provided so as to extend downward. The fourth plate member 28 b is provided in a posture along the vertical direction, and an upper end portion thereof is bolt-connected to the third plate member 28 a and a lower end portion thereof is connected to the second exhaust path 26.

  In this way, the first support 27 that supports the first exhaust path 24 and the second support 28 that supports the second exhaust path 26 are provided separately. The member to which the first support 27 is connected is the engine mounting frame 3, the member to which the second support 28 is connected is the mounting support 29, and the member to which the first support 27 is connected. The member to which the second support 28 is connected is configured to be a different member.

The flow of the exhaust H and the outside air G in the exhaust device 23 will be described.
The outside air G is caused to flow from the outside air introduction part 25 into the second exhaust path 26 by an ejector effect due to the inflow of the exhaust gas H flowing through the first exhaust path 24 into the second exhaust path 26. Since the gap S is formed between the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26, the outside air G is introduced through the gap S. The outside air G having a sufficient flow rate can be introduced from the outside air introduction unit 25. Since the outside air G introduced from the outside air introduction section 25 is directly introduced into the second exhaust passage 26 as it is, the second exhaust passage 26 is not heated by the exhaust H flowing through the first exhaust passage 24. In FIG. 4, the exhaust gas H is mixed with the exhaust gas H flowing through the first exhaust passage 24. As a result, in the second exhaust passage 26, the low temperature outside air G can be mixed with the exhaust H at a sufficient flow rate, so that the temperature of the mixture K can be sufficiently lowered, and the exhaust temperature to the outside can be reduced. Reduction can be effectively achieved.

  Further, both the first exhaust path 24 and the second exhaust path 26 are constituted by flow pipes, and the center part of the flow path cross section of the first exhaust path 24 and the center part of the flow path cross section of the second exhaust path 26 are Are arranged at the same position, the first exhaust passage 24 and the second exhaust passage 26 are provided. As a result, a gap T is formed over the entire circumference in the circumferential direction between the outer peripheral portion at the downstream end 24 b of the first exhaust passage 24 and the inner peripheral portion at the upstream end 24 a of the second exhaust passage 26. The gap T is configured as an outside air introduction part 25. Therefore, the outside air introduction unit 25 can introduce the outside air G over the entire circumference in the circumferential direction of the outer peripheral portion at the downstream end 24b of the first exhaust passage 24, and ensures a sufficient introduction flow rate of the outside air G. be able to.

[Second Embodiment]
In the first embodiment, with respect to the positional relationship of the first exhaust path 24 and the second exhaust path 26 in the exhaust flow direction, the downstream end 24 b of the first exhaust path 24 and the upstream side of the second exhaust path 26. The first exhaust passage 24 and the second exhaust passage 26 are provided so as to form a gap S between the end portion 26a and the end portion 26a. Instead, as shown in FIG. 5, the first exhaust path 24 and the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26 are located at the same position. A second exhaust path 26 can also be provided.

〔Experimental result〕
Hereinafter, since the experiment for verifying the effect of the exhaust device 23 in the first and second embodiments has been performed, it will be described based on the experiment result.
First, as shown in FIG. 6, the positional relationship (A1 to A4) in the exhaust flow direction between the first exhaust path 24 and the second exhaust path 26 and the length (X1 to X3) of the second exhaust path 26. ) Was changed, and an experiment was conducted on how the ratio R of the outside air introduction flow rate from the outside air introduction unit 25 to the exhaust flow rate in the first exhaust path 24 changes. In FIG. 6, the length of the second exhaust path 26 is taken on the horizontal axis, and the ratio R of the outside air introduction flow rate to the exhaust flow rate is taken on the vertical axis.

Regarding the positional relationship of the first exhaust path 24 and the second exhaust path 26 in the flow direction of the exhaust, in A1, the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26 A gap S is formed between them. This A1 corresponds to the first embodiment. In A2, the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26 are at the same position. This A2 corresponds to the second embodiment. A3 and A4 are comparative examples, and in A3, the upstream side end portion 26a of the second exhaust path 26 is set to the upstream side of the downstream side end portion 24b of the first exhaust path 24, and the first exhaust path 24 and the second exhaust path. A portion having a double tube structure with the passage 26 is formed. In A4, as in A3, a portion that forms a double tube structure of the first exhaust passage 24 and the second exhaust passage 26 is generated, and the length of the portion that forms the double tube structure is longer than A3. Try to be long.
In addition, the length of the second exhaust passage 26 is set to satisfy the relationship of X1 <X2 <X3.

In FIG. 6, the outside air introduction flow rate increases as the ratio R of the outside air introduction flow rate to the exhaust flow rate increases. Therefore, as for the positional relationship of the first exhaust path 24 and the second exhaust path 26 in the exhaust flow direction, a portion having a double pipe structure of the first exhaust path 24 and the second exhaust path 26 is generated. The case where the downstream end 24b of the first exhaust passage 24 and the upstream end 26a of the second exhaust passage 26 are at the same position (A2) and the first exhaust, compared to the arrangement (A3, A4). When the gap S is formed between the downstream end 24b of the passage 24 and the upstream end 26a of the second exhaust passage 26 (A1), the outside air introduction flow rate increases.
Further, the outside air introduction flow rate increases as the length of the second exhaust path 26 increases.

  Here, as shown in FIG. 7, the horizontal axis indicates the positional relationship (A1 to A4) of the first exhaust passage 24 and the second exhaust passage 26 in the flow direction of the exhaust, and the ratio of the outside air introduction flow rate to the exhaust flow rate. Take R on the vertical axis. As a result, the downstream end 24b of the first exhaust path 24 and the upstream end 26a of the second exhaust path 26 are the same rather than a double pipe structure of the first exhaust path 24 and the second exhaust path 26. It is understood that the outside air introduction flow rate is increased when the gap S is formed between the downstream end 24b of the first exhaust passage 24 and the upstream end 26a of the second exhaust passage 26. . As a result, the downstream end 24b of the first exhaust passage 24 and the upstream end 26a of the second exhaust passage 26 are located at the same position (second embodiment), or the downstream end of the first exhaust passage 24. When the gap S is formed between the portion 24b and the upstream end portion 26a of the second exhaust passage 26 (first embodiment), a sufficient amount can be secured as the outside air introduction flow rate, and the exhaust temperature can be reduced. Reduction can be effectively achieved. Further, in the first and second embodiments, it is possible to increase the outside air introduction flow rate by making the length of the second exhaust passage 26 as long as possible.

  Incidentally, as described above, the positional relationship of the first exhaust passage and the second exhaust passage in the flow direction of the exhaust, the length of the second exhaust passage, and the exhaust flow rate from the outside air introduction portion with respect to the exhaust flow rate in the first exhaust passage. Regarding the relationship with the ratio of the outside air introduction flow rate, it has been confirmed by experiments that the same tendency is exhibited even if the wind speed of the exhaust gas from the exhaust gas purification processing device 21 is changed.

  As another experiment, when the cross-sectional area (d1, d2) of the first exhaust path 24 and the cross-sectional area (D1, D2) of the second exhaust path 26 are changed, the first exhaust path 24 is changed. How the ratio R of the outside air introduction flow rate from the outside air introduction portion 25 to the exhaust flow rate at the bottom changes, and how the exhaust temperature at the center of the cross section of the second exhaust passage 26 changes. The experiment was conducted. The flow passage cross-sectional area of the first exhaust passage 24 is d1 <d2, and the flow passage cross-sectional area of the second exhaust passage 26 is D1 <D2.

In FIG. 8, the flow path cross-sectional area of the first exhaust path 24 is taken on the horizontal axis, and the ratio R of the outside air introduction flow rate to the exhaust flow rate is taken on the vertical axis. In FIG. 9, the flow path cross-sectional area of the first exhaust path 24 is taken on the horizontal axis, and the exhaust temperature at the center of the flow path cross section of the second exhaust path 26 is taken on the vertical axis.
As shown in FIGS. 8 and 9, when the flow passage cross-sectional area of the first exhaust passage 24 is reduced (d1) and the flow passage cross-sectional area of the second exhaust passage 26 is increased (D2), The ratio R of the outside air introduction flow rate is increased, a sufficient outside air introduction flow rate can be secured, and the exhaust temperature is also sufficiently lowered. Accordingly, it is considered that the larger the cross-sectional area of the outside air introduction portion 25, the greater the outside air introduction flow rate can be increased, and the exhaust temperature can be effectively reduced.

Here, as shown in FIG. 10, the ratio of the cross-sectional area of the outside air introduction part 25 to the cross-sectional area of the first exhaust path 24 is defined as an area ratio P, and the area ratio P is taken on the horizontal axis, When the ratio R of the introduction flow rate is taken on the vertical axis, it can be seen that the ratio R of the outside air introduction flow rate to the exhaust flow rate increases as the area ratio P increases.
When the ratio R of the outside air introduction flow rate to the exhaust flow rate is R = 1, the exhaust flow rate and the outside air introduction flow rate are the same, and it is considered that the exhaust temperature can be sufficiently lowered. It is preferable that the ratio R of the outside air introduction flow rate to the area ratio is 1 or more. Therefore, in the first and second embodiments, the cross-sectional area of the outside air introduction unit 25 is set such that the flow rate of the introduction from the outside air introduction unit 25 is the same as that of the first exhaust passage 24 with respect to the cross-sectional area of the first exhaust passage 24. The exhaust gas flow rate is set to be a set multiple (for example, 3 times) or more.

[Another embodiment]
In the first and second embodiments, various shapes can be applied to the shapes of the first exhaust path 24 and the second exhaust path 26. For example, the first exhaust path 24 and the second exhaust path are formed by square pipes. The path 26 can also be configured.

  The present invention mixes a first exhaust passage through which exhaust from an engine is circulated, an outside air introduction portion that introduces outside air, exhaust gas that has circulated through the first exhaust passage, and outside air introduced from the outside air introduction portion. A second exhaust passage that exhausts to the outside and can be applied to various exhaust devices of a tractor that can effectively reduce the exhaust temperature.

8 Engine bonnet 9 Engine 23 Exhaust device 24 First exhaust passage 24b Downstream end 25 of first exhaust passage External introduction portion 26 Second exhaust passage 26a Upstream end 27 of second exhaust passage 27 First support 28 Second Support S S Gap T Gap

Claims (5)

A first exhaust passage through which exhaust from the engine is circulated, an outside air introduction portion that introduces outside air, and exhaust gas that has circulated through the first exhaust passage and outside air introduced from the outside air introduction portion are mixed and exhausted to the outside. A tractor exhaust system comprising a second exhaust path,
The first exhaust path and the second exhaust path are disposed in a state where the downstream end of the first exhaust path and the second exhaust path extend in the front-rear direction,
The flow passage cross-sectional area of the second exhaust passage is configured to be larger than the first exhaust passage,
The positional relationship in the flow direction of the exhaust between the first exhaust path and the second exhaust path is such that the outer periphery at the downstream end of the first exhaust path and the inner periphery at the upstream end of the second exhaust path. Or the first exhaust passage so that the downstream end portion of the first exhaust passage and the upstream end portion of the second exhaust passage are in the same position in a state where the space is open to the outside. The first exhaust passage and the second exhaust passage are provided so as to form a gap between the downstream end portion of the second exhaust passage and the upstream end portion of the second exhaust passage,
The outside air introduction portion is configured by a gap formed between an outer peripheral portion at a downstream end portion of the first exhaust passage and an inner peripheral portion at an upstream end portion of the second exhaust passage ,
A tractor exhaust system in which a downstream end of the first exhaust passage and the second exhaust passage are disposed below an engine bonnet that covers the engine . The first exhaust path and the second exhaust path are provided so as to form a gap between the downstream end of the first exhaust path and the upstream end of the second exhaust path ;
Before Symbol exhaust system of the tractor according to claim 1 which is disposed on the front side in the vehicle body longitudinal direction with respect to the second exhaust passage is the first exhaust passage.   The first exhaust passage and the second exhaust passage are circumferentially arranged between an outer peripheral portion at a downstream end portion of the first exhaust passage and an inner peripheral portion at an upstream end portion of the second exhaust passage. The exhaust device for a tractor according to claim 1 or 2, wherein the exhaust device is disposed so as to form the outside air introduction portion over the entire circumference.   The tractor exhaust device according to any one of claims 1 to 3, wherein a first support body that supports the first exhaust path and a second support body that supports the second exhaust path are provided separately. .   The cross-sectional area of the outside air introduction part is greater than a set multiple of the flow rate cross-sectional area of the first exhaust path so that the introduction flow rate from the outside air introduction part is equal to or greater than the exhaust flow rate in the first exhaust path. The exhaust device for a tractor according to any one of claims 1 to 4, wherein the exhaust device is configured as follows.

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